Sci-fi style robots, fault-hearing engineers, anti-static shoes – Canon's Utsunomiya lens factory is a hotbed of innovation and precision. Canon's L-series lenses are known around the world for their professional-quality build and sharp results, but to produce such outstanding lenses requires impressive levels of craftsmanship, attention to detail, and a few surprising practices.

From the bespoke machinery that perfectly moulds the glass, to the engineers who hand-test the lenses, nothing is overlooked. Here, we uncover 10 top facts from Canon's lens factory in Utsunomiya, Japan, that highlight the craft behind these pro-level lenses.

1. Japanese engineering is everywhere

Around 100km north of Tokyo, Japan (a 50-minute journey by bullet train), lies Canon's Utsunomiya lens factory, the main production hub for L-series lenses. Measuring 160 x 200 metres, the factory covers the area of 4.7 football pitches – and has capacity to fit four Airbus A380 planes inside it. Lens manufacture here is so precise that the plant's internal temperature is regulated to within 0.5°C. All workers and visitors wear protective clothing, including anti-static shoes in the main facility and special clean-room slippers in assembly and testing areas. Everyone also has to pass through an 'air shower' before entering dust-free environments, to protect the manufacturing process.

2. Lens experts can hear faults

While much of the lens manufacturing process is automated, expert craftsmen, called Takumi, play an important role in lens creation. Toshi Saito, one of Canon's lens Takumis, brings over 25 years of experience, skill and even his senses to the role. "When the lens is touching the diamond plate I know what sound it should make, so when it's slightly off, I can detect it with my hearing," he says. As well as working on lenses by hand, Toshi uses his experience to 'train' automated machinery to reproduce the tolerances and accuracy required by the designers.

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3. Lens polishing tools are made with diamonds

Lenses are designed using CAD software that accounts for the physical and optical properties of the different glasses being used – whether the metal oxides and other material particles are arranged in regular (crystal), irregular (glass) or in between (amorphous) patterns defines how the glass behaves. Each glass element in a lens is ground, smoothed and polished to the precise profile required, with polishing tools made from diamond grindstone-covered plates. Firstly, the glass is ground blank, to remove excess thickness, before it is smoothed, to reduce cracks. The third stage is centring, during which the edges of the lens are ground down to ensure the lens is optically centred. Then it's polished further to smooth tiny surface cracks, finalise the shape, and turn it transparent. The lens is then ready for inspection.

4. Aspherical lenses are made by melting glass

Glass is the best material for making lenses – being transparent, relatively easy to shape and thermally and chemically stable – but it can be hard to work with. Most elements in a camera lens are spherical but sometimes the optical designs call for more complex, non-spherical elements. These aspherical lenses are extremely difficult and expensive to manufacture using traditional grinding and polishing techniques, but Canon has its own glass-moulding machinery at the Utsunomiya plant to make them from molten glass billets. Each mould is designed with an extremely high level of precision, to take into account the exact changes in dimensions that will take place as the glass cools down and hardens.

5. Sci-fi robots roam the factory

With long distances to cover on the Utsunomiya factory floors, automated delivery robots speed around, carrying their precious cargo to various stations. They follow yellow tracks painted on the floor and are aware of each other's presence, diverting along passing lanes to get around each other. They even have automatic collision detection sensors to stop them from crashing into people or objects; ensuring glass and lens parts reach their destinations safely.

6. Lens polishing machines self-correct

Automation also helps in the manufacturing process, such as when Canon's lens polishing machines come into play. Operators oversee the process, ensuring the machines, which have been developed in-house, are functioning correctly. But the machines can also self-correct – they automatically measure lens elements at two points in the production process, and act on any deviations from the design profile, correcting that lens and tweaking parameters so that the next one they produce is as close as possible to the design ideal. Despite the importance of automated technology, there are some things, such as the expertise of the Takumi, that can't be replaced. Every Canon L-series 16-35mm lens – not just the samples – is tested and calibrated by hand using a complex nine-point optical test process, ensuring that each lens meets the high standard expected in the premium line.

7. Lens measurements are incredibly precise

Canon's highest precision lenses are constructed for the 4K/8K broadcast industry and have a manufacturing deviation of less than 30 nanometres (one nanometre is one millionth of a millimetre). To visualise this, imagine a lens large enough to cover the Maracana Stadium in Rio de Janeiro, Brazil, which is 300 metres wide. Across its entire surface, this giant lens would demand deviations of less than the thickness of a plastic bag (0.03mm).

8. The hardest lens to make is...

Is building the widest zoom lens in the world the greatest challenge? The Canon EF 11-24mm f/4L USM lens – which offers an angle of view of 117° at its widest setting and has a huge convex front element, with four aspherical elements – might appear to be the most difficult lens to make, but Toshi says not. "It was a slight challenge at the beginning, but not so much of a difficulty." In fact, the hardest lenses to make are Canon's long L-series telephoto lenses, such as the Canon EF 100-400mm f/4.5-5.6L IS II USM. With their complex internal movements, they are the most time-consuming to assemble – taking four times longer than zoom lenses such as the Canon EF 16-35mm f/2.8L III USM.

9. The innovation never ends

Canon invented image stabilisation. We use lens- rather than sensor-based image stabilisation for EOS DSLRs because to produce the clearest viewfinder image possible, you have to stabilise the glass. We also use new optical materials in the Canon EF 35mm f/1.4L II USM lens and other specialised lenses. One of these materials is BR (Blue Spectrum Refractive optics), made from a resin that we developed. These BR lens elements provide strong blue light refraction, and reduce chromatic aberration better than regular glass elements.

10. Canon lenses could (probably) cover half the world

In October 2017, Canon hit a production milestone of 130 million EF lenses, which would likely stretch halfway around the world if they were all laid end to end. With these millions of lenses, we have continually introduced new technologies. We bring these new developments to the L-series lenses first, with the aim of then passing these innovations down the line to mid-range products and, where possible, entry-level cameras, so that everyone benefits from the latest developments.